1. Technical Field
The present invention relates to a system for improving the quality of waters and fluids produced from petroleum and gas well drilling and recovery operations, mining operations, and during other industrial activities, and specifically to a method that does not involve the use of traditional filtration or separation methods. The present system separates contaminants from the water and field produced fluids utilizing a pressure separation apparatus which can also create and facilitate hydrodynamic cavitation conditions within the produced fluid. This results in the improved separation and removal of particulates and dissolved constituents from the fluid.
2. Description of Related Art
The safe and effective removal of contaminants from water and other fluids is a consistent problem faced by many industries. The impurities accumulated by water and other fluids during the hydrologic cycle, industrial processes and manufacturing activities may appear in both suspended and dissolved forms. Suspended solids may be generally classified as particles larger than molecular size (i.e. particle sizes greater than 10−3 mm), which are supported by buoyant and viscous forces existing within water. Dissolved materials (i.e. particle sizes less than 10−3 mm) consist of molecules and ions, which are held by the molecular structure of water.
The presence of suspended and/or dissolved solids in water, wastewater and other fluids is undesirable for several reasons. The presence of visible suspended solids may be aesthetically displeasing. Likewise, the presence of suspended and/or dissolved solids allows for the adsorption of other chemicals or biological matter into the fluid. Due to the standards promulgated by government agencies, excessive contaminants must be removed from potable water, wastewater and other types of contaminated fluid streams before the effluent may be discharged to the environment or recycled for reuse. If established discharge-contamination levels are exceeded, governmental authorities and agencies may impose surcharges and penalties on the entity responsible for the discharge of fluids which does not meet or exceed the appropriate standard of quality.
Both terrestrial and offshore oil and gas fields produce large quantities of contaminated water that can have significant environmental effects if they are not handled, remediated and discharged properly. In a typical petroleum formation, formation water lies adjacent the formation layer containing the desired hydrocarbons (e.g. oil and natural gas). As a result, when these hydrocarbons are removed from the formation via the wellbore, formation water is brought to the surface along, with the hydrocarbons. If required and in order to achieve maximum recovery, water will be injected into the formation to provide additional motive force to recover the hydrocarbons from the formation. As a result, increasing volumes of both formation water and injected water are produced (also referred to collectively as “produced water”) in the recovery of oil and gas from the formation. The treatment of produced water is a major component of the cost of producing oil and gas.
From the present day oil and gas operations occurring around the world, the volume of produced water is certainly not insubstantial. For example, 253 million tons of produced water is estimated to have been generated from offshore drilling rigs located in the UK sector of the North Sea in the year 1998. This produced water was then treated according to processes in place at the time and discharged into the ocean. However, the discharged water still contained an average oil concentration of 22 ppm at the time of discharge into the ocean.
In typical petroleum recovery operations, produced water is separated from the oil or gas recovered from the formation, treated to remove any hydrocarbons or other contaminants mixed or dissolved therein, and then discharged to the surface, ocean, or reinjected into the formation or well depending on the location of the well. Produced water characteristics and physical properties vary considerably depending upon the geographic location of the field, the geological formation with which the produced water has been in contact for thousands for years, and the type of hydrocarbon product being produced. The contaminants of produced water include salt content expressed as salinity, conductivity, or total dissolved solids (“TDS”). Other contaminants may include slurries having dispersed oil droplets, dissolved organic compounds including dissolved oil, drilling fluids, polymers, well treatment and workover chemicals, and other organic and inorganic compounds that can lead to toxicity. Some of these are naturally occurring in the produced water while others are related to chemicals that have been added for drilling and well-control purposes. Further, contaminants can also include dissolved gases including hydrogen sulfide and carbon dioxide, bacteria and other living organisms, and dispersed solid particles. Produced waters also typically exhibit low concentrations of dissolved oxygen and non-volatile dissolved organic materials. Because of the contaminants in produced water, it requires no large amount of thought to surmise that the direct release or reinjection of untreated produced water into the ocean, upon land, or into the subsurface formation would have damaging effects on the environment and pose health risks to animals and humans in both the short and long term.
Due to the presence of the aforementioned undesired constituents/contaminants in produced water, administrative and other governmental agencies have enacted legislation which prohibits the discharge of produced waters containing concentrations of such contaminants that are greater than a prescribed concentration level. For example, the United States Environmental Protection Agency currently limits the content of “oil and grease” in produced waters to 29 ppm (parts per million) with a maximum of 42 ppm. If oil and gas producers discharge produced waters that contain concentrations of specified contaminants which exceed the specified maximum discharge concentrations, severe fines and potential criminal penalties can result. Therefore, the need for a system which can efficiently and economically remove contaminants from produced waters, as dictated by governmental statutes and agencies, is of paramount importance to industry.
One prior art solution for treating produced water involves pumping the water through disposable filters to filter and remove the suspended solids. There are several problems with this prior art solution. First, once the disposable filters have been used they are typically considered hazardous waste and they must be sent to special disposal facilities for disposal after use further depleting the increasingly diminishing landfill space available. Second, the disposable filters are themselves relatively costly and therefore do not provide an economical treatment solution. Third, the constant changing of used disposable filters with clean or new disposable filters is labor intensive. Fourth, the disposable filters have a relatively short lifespan as they (1) are constructed of paper-based material which is easily degraded by contaminants, (2) are unable to continually support the sheer mass of the contaminants that are loaded onto the filters during filtration operations, and (3) cannot withstand typical backwash cleaning pressures Consequently, a need exists for a way to minimize or eliminate the need for disposable filters in the removal of suspended solids from waste streams such as produced water.
Another problem encountered in removing contaminants from fluids is the expense and difficulty in designing a system that can remove contaminants that vary widely in chemical and physical make-up. As alluded to above, the chemical make-up of contaminants ranges widely from dissolved oil and brine to bacteria in produced waters. Similarly the physical make-up of the contaminants varies in particle size from the ionic range (brine) to the micro and macro particle range (oil droplets). Such a wide range of contaminants presents several challenges in treating produced waters. For example, slurries and biological contaminants can plug filtration equipment, and separation of metals from contaminated water typically requires expensive chemical precipitation processes. These are just a sampling of the difficulties encountered in the treatment of industrial waste water which illustrates the complexity and expense of treatment facilities that must be constructed to treat such waste water in lieu of disposable filters. Because such treatment facilities are complex, they are typically not mobile, therefore requiring industrial waste water be stored on-site and then shipped to a treatment facility. For example, produced water is often stored in a tank near oil or gas well until the waste can be trucked to a treatment or injection facility. Similarly, treated water for recovery operations must be trucked into and stored near the wellhead for petroleum recovery operations such as drilling and fracturing wells. Consequently, a need exists for an improved method and apparatus for treating contaminated water. In one aspect, the apparatus and method should be mobile and able to be economically installed near the location where the contaminated water is produced. In one aspect, the apparatus and method should provide sufficient treatment to meet regulatory standards required to permit discharge of water directly into the environment. In another aspect, the method and apparatus should be able to provide for the treated water needs of the facility where the apparatus is located. As such, a need exists in the art for a portable, highly efficient filtration apparatus and method which can separate suspended and dissolved solids and other contaminants in a variety of environments. Further, a need exists for an improved apparatus and method of removing particles from fluids in either a liquid or gaseous state. Further, a need exists for an apparatus and method which can consistently remove particles of a desired size so as to efficiently and consistently reduce the chance of the imposition of a surcharge for violating quality control standards and the release of untreated effluents.